(1) Field of the invention.
This invention relates to engine ignition analyzers; and, in particular, to circuitry for processing signals generated by ignition firing for use in such equipment.
(2) Prior art.
A standard accessory for use with the conventional engine analyzer is a strobe or timing lamp which provides a pulsed light of very short duration. In a typical internal combustion, a fixed reference mark is provided on the engine housing adjacent the flywheel which carries another reference mark. When these two reference marks are aligned, the engine is in the top dead center position which normally corresponds to the firing time for the number 1 cylinder.
The conventional strobe lamp is triggered by the number 1 cylinder firing signal during running of the engine producing a repeating short light pulse permitting visual determination by the mechanic of the actual engine flywheel position with respect to the fixed reference mark for any engine speed. The mechanic notes the difference between the two reference marks, typically in degrees scribed next to the reference mark to determine the amount of advance of number 1 cylinder firing signal with respect to top dead center.
In improved timing lamps, a variable delay was introduced into the timing lamp so that the lamp trigger pulse was delayed with respect to the number 1 cylinder firing signal. In using this improved lamp, the mechanic adjusts the delay so that the two reference marks are aligned when the lamp is triggered, and reads the calibration of the delay adjustment in terms of degrees of advance.
Some qualities and features which characterize these improved lamps include:
(A) DELAY ANGLE INDEPENDENT OF RPM for a delay control setting.
(B) PROVISION FOR ANGLE SETTING AND READOUT BEFORE OR AFTER OPERATION ON AN ENGINE.
(C) BROADNESS OF RPM range for accurate readings.
(D) SPARK IGNITION NOISE REJECTION PREVENTING IRREGULAR DELAYS AND EXTRANEOUS LIGHT PULSES.
Problems commonly found in lamps however are: delays controlled for fixed time, not fixed duty cycle, and readout indicators such as meters that only indicate a control setting while the engine is running. Because readings are commonly taken at high engine RPM it is desirable to minimize the time to make measurements. If the lamp can be preset to the specified engine advance angle the time to visually locate the mark can be reduced and then the RPM can be immediately dropped since the reading will be held by the indicator.
Meters present some particular limitations on a timing lamp because of balance, parallax and motion which all add to the readout error. Sensitivity to mechanical shocks and magnet weight tend to limit durability and necessitate careful handling.
The environment of testing the ignition firing of an engine is very noisy and the problem of reducing the effects of electrical noise is difficult to solve. Further, the problem is significant because an accurate indication for the number of degrees of advance is increasingly important as automobile engines increase in complexity and pollution control equipment is added. There has been no satisfactory solution to the problem of providing a device having a commercially attractive price which is sufficiently noise resistant when readings of degrees of advance are made. Again, this is particularly true when the degrees of advance are relatively small or close to 0.